Process of forming acetic acid from methanol and carbon monoxide



Patented June 5, 1934 UNITED STATES PATENT? OFFRC PROCESS OF FORMINGACETIC ACID FROM METHANOL AND CARBON MONOXIDE poration of Tennessee NoDrawing. Application March 21, 1930, Serial No. 437,930

7 Claims. (Cl. 260-416) This invention relates to methods and means forthe formation and manufacture of acetic acid. One of the principalobjects is to enable acetic acid to be formed from methyl alcohol, watervapor, and carbon monoxide.

Another object of the invention is to provide a process for convertingaliphatic alcohol to the next higher acid in the same chemical series.

Another object of the invention pertains to a 10 process for convertingan alcohol to the next higher acid in the same chemical series by theuse of heat and pressure.

Another object of the invention relates to a process for converting analcohol to the next higher acid in the same chemical series by theapplication of heat and pressure in the presence of a selected catalyst.

Another object of the invention is to improve, simplify and render moreefficient and economical the conversion of an alcohol to the next higheracid in the same chemical series by causing any unreacted gases orvapors coming from the catalyst to be returned or recirculated throughthe catalyst, without interrupting the circulation and without releaseof the pressure, thereby effecting a more complete conversion of thealcohol to the acid.

Other objects and advantages other than those hereinbefore mentionedwill be specifically pointed out and will be apparent from thediscussion and description herein given.

This invention resides specifically in the combination, sequentialoperation, and relative application of steps or parts of steps, as willbe fully indicated hereinafter.

l-leretofore it has been shown that alcoholates, such as sodium ethylatecan be caused by proper treatment to combine with carbon monoxide toyield a product which is a salt of the next higher acid in the samechemical series from which the original alcoholate is derived (e. g.sodium propionate). The present invention, together with the inventiondisclosed in our copending application for Letters Patent Serial No.379,312, filed July 18, 1929, enables the same result to be attained bya novel and simplified process. It has been found that methyl alcohol,for example, under certain conditions will react with carbon monoxide toform acetic acid without producing during such formation either analcoholate or a salt of the acid so formed. By following the processaccording to the present invention, therefore, it is possible to makecommercial as well as pure acetic acid on a large scale and at greatlyreduced costs.

In our copending application for Letters Patent aforementioned wedisclose an illustration of one manner of carrying out the process whichwe will briefly repeat here so that the same may be contrasted with thesubject matter of this present invention. We there said that methylalcohol vapor and carbon monoxide gas are mixed and compressed under ahigh pressure, which pressure is usually about 250 atmospheres, althoughpressures ranging from 50 to 400 atmospheres, can be successfully usedwithout departing from the scope of the invention. This subjection ofthe mixture to pressure is said to be preferably effected at atemperature sufiiciently high to prevent condensation of the alcoholvapor. The compressed mixture is then passed at a selected velocity overa heated catalyst. As the gaseous mixture comes out of the catalyst tubeit is passed through a condenser, or is subjected to other means forcausing condensation of the acetic acid vapor formed. Thereafter, thecondensed vapor and gas are passed through a suitable device, trap orseparator, to separate the condensed acetic acid from the uncondensedgas or vapors, which latter are mainly comprised of carbon monoxide, andpossibly methyl-ether, and some unconverted methyl alcohol. Theseuncondensed gases we proposed, in our prior application, to remove inany suitable manner, preferably in a continuous process by allowing themto expand through a suitable expansion valve until atmospheric or otherdesired pressure is attained. We further stated that if desired insteadof reducing the pressure of the uncondensed gases said gases might bemixed with a predetermined amount of steam and then passed through asecond catalyst tube containing a suitable catalytic agent, such asalumina. The passage through the second catalyst tube causes any freemethylether which may be present to react with the water vapor andregenerate methyl alcohol as a vapor, which is later condensed after thegases leave the second catalyst tube, by any well known method ofcondensation. Methyl alcohol which is thus regenerated, we have stated,may be used in the process, if desired. The liquid which is condensedand trapped out after passing over the first catalyst contains, as abovedescribed, the acetic acid which, if desired, may be concentrated by anystandard process of distillation. We also stated that as one example ofa catalyst that has been found eifective in the formation of aceticacid, we might mention the use of syrupy phosphoric acid, although anyother equivalent, preferably a dehydrating catalyst, might be employedand we stated that the catalyst is preferably preheated to a temperaturea little over that at which it is to be used in the catalyst tube, anddesirably exposed to the reacting gases over as large a surface aspossible in order that a maximum of catalytic action be obtained whenthe gases pass through the catalyst tube. We also specified in saidapplication a practical manner of attaining this last desirable result,and discussed the range of temperatures at which the reaction might bepreferably carried out. We also disclosed the fact that we had foundthat a mixture of carbon monoxide and carbon diordde, instead of carbonmonoxide alone, tends to reduce the formation of the carbon in thecatalyst tube by providing an over sufiiciency of carbon monoxide, thatis, the carbon dioxide provided tends to combine with any free carbonthat may be present to yield carbon monoxide according to the chemicalequation:

In carrying out our Work further on the produc tion of acetic acid frommethanol by this method of synthesis we have now found that aqueoussolutions of methyl alcohol and mixtures of water vapor and methylalcohol vapor react as well as the concentrated methanol when incombination with carbon monoxide in the presence of a proper catalyst,such as syrupy phosphoric acid or the like. The catalyst to present amaximum catalytic action should preferably be spread out upon achemically inert solid substance, such as silica gel and/or charcoal orthe like. The operation just mentioned is also to be carried out at apressure usually about 250 atmospheres although pressures ranging from50 to too atmospheres can similarly be successfully used withoutdeparting from the scope of the invention, and at a temperature between100 C. to 600 C. We have found further that the methyl-ether, which isformed in the reaction as a by-product, and which we stated to bepossible of recovery as methanol, might be recovered as dilutedmethanol, as an active agent, and, further, that the water vapor ordilute methanol might be introduced into the chamber proper. Weare notsure whether further chemical action or reaction is produced by thepresence of the water element of the aqueous methanol solution, or bythe presence of water vapor in said aqueous solution, or in the vapor ofmethyl alcohol, or by mixtures of water vapor and methyl alcohol or itsvapors. However, we have found that acetic acid may be produced therebyas readily as that attainable from the use of concentrated or dilutemethanol. Consequently, according to our present invention, we haveprovided a new, simple, inexpensive and efficient method of producingacetic acid synthetically. In other words, we have discovered that theconcentrated methanol heretofore employed may be replaced, in themanufacture of acetic acid, by diluted or water diluted methanol andthat the same desirable results are obtain able. While it is possiblethat it is the methyl alcohol content of the aqueous solution whichperforms the major portion of the useful work in the chemical. reaction,yet we have discovered that the presence in the chemical reaction of thewater diluent yields a most desirable quantity of acetic acid, of adesirable quality, and in a quick and very cheap way. We have found thatthe results obtainable with the use of the diluted product enables us tomore efficiently effect the mixture of the methyl alcohol element withthe carbon monoxide or the aqueous vapor mixture,

inasmuch as the diluted methyl alcohol is more prone to combine, undersome conditions, with the carbon monoxide gas than is the concentratedliquid methyl alcohol with the same carbon monoxide gas.

While we have mentioned the use of carbon monoxide and carbon dioxidegases as suitable for carrying out our present invention, it is to beunderstood that gaseous mixtures containing such gases may likewise beemployed with good results. We have also discovered that bypredeterminedly varying the proportions of aqueous and methyl alcoholvapors we are able to preserve and prolong the life of the catalyticagent used.

We have further discovered that the conversion of an alcohol to the nexthigher acetic acid in the same chemical series in accordance with ourinvention, may be greatly simplified and rendered more efiicient andeconomical, by returning or recirculating to the action of the catalystthe unconverted and unreacted gases and. vapors without permitting theexpansion of such gases or vapors, or release of the pressure thereon.This results in a more complete conversion of the alcohol and eliminatesentirely the production of lay-products such as methyl-ether, andobviates any necessity of converting that by-product into methyl alcoholfor use over again in the process. This also makes it unnecessary tohandle, recover or recompress large volumes of gas, as has beennecessary heretofore. Any condensed acid produced may be trapped 0rdrawn off from time to time, without interrupting the circulation andrecirculation of the reacting gases or vapors. In order to maintain theproper ratio of the reacting agents the condensed acid drawn off fromtime to time should be replaced in the circulating system by freshsupplies of mixtures of aliphatic alcohol and water, or of the vaporsthereof, and carbon monoxide gas.

It is to be understood that the following claims are intended to coverall of the generic and specific features of the invention hereindescribed.

What we claim for United States Letters Patent is:

1. lhe process of forming acetic acid which consists of mixing methylalcohol vapor, aqueous vapor and carbon monoxide under pressure and at asufficiently high temperature to prevent condensation of said alcoholvapor, passing said mixture over a heated dehydrating catalyst andthereafter condensing the acetic acid out of the gaseous mixture, andwithout reducing pressure mixing with the uncondensed gaseous mixture aquantity of steam and passing said steam mixture over a methanolcatalyst.

2. The process recited in claim 1 characterized in that methyl alcoholvapor is mixed with the carbon monoxide while the mixture which iscondensed is removed and concentrated to yield concentrated acetic acid,and the methyl alcohol which is regenerated is diluted and reused in theprocess.

3. The process of forming acetic acid which consists in combining dilutemethyl alcohol vapor, aqueous vapor, and carbon monoxide gas underpressure and at a sufliciently high temperature to prevent condensationof said alcohol vapor, passing said mixture over a catalyst of syrupyphosphoric acid. spread upon silica gel, thereafter condensing thegaseous mixture forming acetic acid, removing the portion of the gaseousmixture which is condensed and concentrating it to yield concentratedacetic acid, maintaining pressure and mixing with the uncondensedmixture a quantity of steam, and passing said mixture of gases and steamthrough a second catalyst tube to remove free methyl-ether therefrom.

4. The process of manufacturing acetic acid from dilute methanol whichincludes mixing dilute methanol vapor with aqueous vapor and a gascontaining carbon monoxide and carbon dioxide and passing the portionsof said mixtures over syrupy phosphoric acid and condensing out aceticacid and passing the remaining mixture over alumina in succession.

5. The process of forming acetic acid in accordance with claim 4characterized in that the mixture is passed over the syrupy phosphoricacid and a part of the reaction product is passed over the alumina.

6. The process of producing acetic acid from methanol which consists informing a mixture of methyl alcohol vapor, aqueous vapor and carbonmonoxide gas, passing said mixture under pressure over a dehydratingcatalyst, condensing out the acetic acid thereby formed, concentratingthe acetic acid, converting into methanol any methylether which may bepresent in the residual gases after condensing out the acetic acidtherefrom, by mixing said methyl-ether with steam, passing the resultingmixture over a methanol catalyst, and then condensing out the methanoland diluting the same for re-circulation through the system.

7. The process of producing acetic acid from methanol which consists informing a mixture of dilute methyl alcohol vapor, aqueous vapor andcarbon monoxide gas passing said mixture under pressure over a heatedcatalyst consisting of syrupy phosporic acid, condensing out from theresulting mixture the acetic acid formed, converting into methanol anymethyl-ether which may be present in the residual gases after removal ofthe acetic acid, by mixing said methyl-ether with steam, passing saidmixture over a methanol catalyst, consisting of alumina, removing theresulting methanol and diluting it for recirculation through the system.

JOSEPH C. CARLIN. NORMAN W. KRASE.

